What I meant to say was a container bog - and having that container all within the big liner. Not using a preformed pond as the bog. Sort of using a container to hold the bog gravel (filter media) rather than trying to build a wall in a small area.I'm not a fan of preforms at all. They create more work then is a epdm liner. Like how do you have water leave the preform? Cut one edge lower ? This will compromise their stability in a big way. The plastic is like metal the more bends the stronger the plastic is. Cut the rolled edge off and it's no longer that strong.
Try to secure liner to the preform? This will fail its not if, it's when, how long will it last. A preform that's lined could hold the water and have line liner drop at where the waterfall would be.
I know they are pricey but a biofalls would save a lot of time.
But I also agree that a bio falls for a small pond would save lots of time -- which leads me back to the idea of a kit.